X-ray diffraction data on a rhombohedral crystal form of the Southern bean Mosaic plant virus (SBMV) has been collected to 22 A resolution. This data is being processed and should shortly lead to a very low resolution electron density map of this small spherical RNA virus. This should show the rough distribution of protein and perhaps the nucleic acid within the virus. Resolution is to be extended in stages to eventually 3 A, although that may take many years. A different orthorhombic form of SBMV is also being investigated. Although this work has not progressed as far, it may present eventually fewer technical problems. Simultaneously similar and parallel work on the common cold virus (l-A, HRV) has commenced. Crystals are available but need to be grown larger. For this purpose it has been necessary to create a tissue culture "factory". Eventually it is hoped to also produce a structure of this virus. A detailed elucidation of a virus structure should lead to a full understanding of its eventual relationship and function in the host cell.